Smooth zooming in viewport
You can do that zooming for sure if you know how to add a new keymap:

Go in that keymap setting panel and choose the 3D-view(global) panel, scroll down to see that Add New Button. Press it, it will give you a None keymap.

Setting up the identifier field with the thing you want, in the zoom case view3d.zoom



And then setup rest of the key setting, you shouldn't need other details setting for your task.